Lightning

Context

• At least 30 people were killed in separate incidents of lightning in various parts of the country in the past 24 hours.

Deaths by lightning

• As a whole, India sees 2,000-2,500 lightning deaths every year on average.
• Lightning is the biggest contributor to accidental deaths due to natural causes.
• A few years ago, over 300 people were reported killed by lightning in just three days — a number that surprised officials and scientists.

Concerns

• Despite of the above figures, lightning remains among the least studied atmospheric phenomena in the country.
• Just one group of scientists, at the Indian Institute of Tropical Management (IITM) in Pune, works full-time on thunderstorms and lightning.
• Occurrences of lightning are not tracked in India, and there is simply not enough data for scientists to work with.
• Often, safety measures and precautions against lightning strikes do not receive as much publicity as other natural disasters such as earthquakes.

What is lightning, and how does it strike?

• Lightning is a very rapid — and massive — discharge of electricity in the atmosphere, some of which is directed towards the Earth’s surface.
• These discharges are generated in giant moisture-bearing clouds that are 10-12 km tall.
• The base of these clouds typically lies within 1-2 km of the Earth’s surface, while their top is 12-13 km away.
• Temperatures towards the top of these clouds are in the range of minus 35 to minus 45 degrees Celsius.
• As water vapour moves upward in the cloud, the falling temperature causes it to condense.
• Heat is generated in the process, which pushes the molecules of water further up.
• As they move to temperatures below zero degrees celsius, the water droplets change into small ice crystals.
• They continue to move up, gathering mass — until they are so heavy that they start to fall to Earth.
• This leads to a system in which, simultaneously, smaller ice crystals are moving up and bigger crystals are coming down.
• Collisions follow, and trigger the release of electrons — a process that is very similar to the generation of sparks of electricity.
• As the moving free electrons cause more collisions and more electrons, a chain reaction ensues.
• This process results in a situation in which the top layer of the cloud gets positively charged, while the middle layer is negatively charged.
• The electrical potential difference between the two layers is huge — of the order of a billion to 10 billion volts.
• In very little time, a massive current, of the order of 100,000 to a million amperes, starts to flow between the layers.
• An enormous amount of heat is produced, and this leads to the heating of the air column between the two layers of the cloud.
• This heat gives the air column a reddish appearance during lightning.
• As the heated air column expands, it produces shock waves that result in thunder.

How does this current reach the Earth from the cloud?

• While the Earth is a good conductor of electricity, it is electrically neutral.
• However, in comparison to the middle layer of the cloud, it becomes positively charged.
• As a result, about 15%-20% of the current gets directed towards the Earth as well.
• It is this flow of current that results in damage to life and property on Earth.
• There is a greater probability of lightning striking tall objects such as trees, towers or buildings.
• Once it is about 80-100 m from the surface, lightning tends to change course towards these taller objects.
• This happens because air is a poor conductor of electricity, and electrons that are travelling through air seek both a better conductor and the shortest route to the relatively positively charged Earth’s surface.

Steps needed to be taken by the Government

• Common Alert Protocol (CAP) system to warn people about impending thunderstorm and lightning strikes.
• "Proactive steps" in building proper infrastructure to ensure safety of its people during natural hazards.
• Building a large number of cyclone shelters along the coastal areas, as done by Odisha.
• Media would need to play a crucial role in creating awareness on natural calamities.
• (IITM), Pune and Earth System Science Organization (ESSO) have developed an app, 'Damini', to monitor lightning activities.
• There is a need for more extensive study in the area and the Ministry of Earth Sciences is carrying out a research project on thunderstorms.

https://indianexpress.com/article/explained/explained-how-lightning-strikes-and-why-it-kills-7401198/